Field
The present application relates to optical isolators and to optical communication systems.
Related Art
Some optical systems can be sensitive to spurious optical reflections from downstream optical components. This is often the case, for example, when a laser is used as an upstream optical source to deliver light to a downstream system. Light from the laser may travel to a downstream optical system, and a portion of the light may back-reflect from a component in the downstream system. The back-reflected light may be fed back into the laser and destabilize the laser operation. In some cases, the back-reflected light may cause amplitude and/or phase fluctuations in the laser output, which can introduce undesirable optical noise into the system. If the optical system comprises a communication link, the noise can result in bit errors.
There are several conventional techniques for optically isolating a component (such as a laser) in an optical system from potential back-reflections arising from downstream optical components. One technique, known as Faraday isolation, employs a magneto-optic polarization rotator and a pair of polarizers. Faraday isolation can require the isolator size to be large (requiring several centimeters of optical path length) to obtain the correct amount of polarization rotation between the polarizers. Faraday isolation may also require a strong magnet to be placed in close proximity to an optical path, which may not be desirable in some applications. Other conventional optical isolation techniques include electro-optic modulation techniques, but some of these systems can also require long path lengths.